Micro-electro-mechanical systems (MEMS) devices have been found in many sensing applications such as airbag sensors, as well as chemical and biological sensors. The use of micro actuators is the key to making MEMS fully active, intelligent “micro-system” devices, capable of both sensing and actuating. Current IC-based micromachining processes, used to fabricate MEMS devices, have certain limitations in achieving the above goals. First, most of the IC-based micromachining processes cannot be used to fabricate complex 3D micro parts with high aspect ratios. Second, only a few semiconductors and other materials can be processed by the current IC-based micromachining for MEMS. Many other important engineering materials, such as smart ceramics, functional polymers, and metal alloys, can not be directly incorporated into MEMS through the conventional IC-based micromachining processes.
As an alternative, an x-ray LIGA (German Lithography, electroforming and molding) process was developed to fabricate microstructures with high aspect ratio. However, the x-ray LIGA process has not found a large number of industrial applications due to its poor industrial accessibility and operational cost. In addition, complex 3D structures can not be achieved by an LIGA process. A novel microfabrication process, the micro stereolithography (μSL) was introduced to fabricate high aspect ratio and complex 3D microstructure by single beam scanning. [Ikuta, K., Ogata, T., and Kojima, S., 1996, “Development of mass productive micro stereo lithography”, Proc. IEEE MEMS'96, pp. 301–305.]
Sophisticated 3D parts can be made by scanning an UV beam on a liquid monomer resin, curing the resin into solid polymer layer by layer, and stacking together all layers with various contours.
Recently, liquid crystal display projection micro-stereolithography has been used by groups in Europe to project a layer image onto the photo-resist. However, due to the large pixel size and very low transmission in UV, the device's resolution is limited and contrast is poor. Macro scale stereo-lithography, on the other hand, has been around for more than 15 years, mainly with single beam scanning, and commercial applications in this area have also been established such as by 3D Systems Inc. Only recently, scientists have started to use digital light processing technology, for example, using a commercial digital micro-mirror display projector from Texas Instrument to do macro-scale stereo-lithography. However, they use mainly a commercial optical setup from Texas Instruments and focus on macro-scale fabrication for structure and automotive applications rapid prototyping. See, also, U. S. Pat. No. 6,200,646 to Neckers et al, entitled: “Method For Forming Polymeric Patterns, Relief Images And Colored Polymeric Bodies Using Digital Light Processing Technology.”